Currently, there is a lot of food that needs to be packed or packaged for shipment using paper or board, however, due to the conservation of food it is necessary to keep it in refrigeration chambers within its packaging. The humidity and temperature conditions under refrigeration may cause a collapse of these packaging materials resulting in loss of stored products, or in an over specification of the board to achieve the required strength with consequent cost increases.
To avoid the deterioration of the packing material either paper or board due to the high humidity conditions, various chemical compositions were studied for applying coatings to prevent moisture passing through the fibers of the paper or board, thus extending their lifetime, increasing the protection of food packaging and reducing costs that may result from failure of the mechanical resistance of the packaging. Some types of coatings such as resins, polymers, copolymers, inorganic and organic compounds are commonly used for paper and board, however, they do not have high moisture resistance values.
The use of nanoparticles for this application represents a great economic advantage for these packages, since the interaction between the cellulose network and the coating nanoparticles can be increased through the incorporation of various functional groups to the nanoparticles, resulting in improved hydrophobic properties due to the chemical interactions between these and the organic matrix. Usually inorganic particles, such as the case of silicon oxide, have a surface with a lower compatibility with organic compounds, either polymers of the polyolefin type or ionics of the amides or amine type, paper fibers or other biopolymers. To achieve a major compatibility it is intended that the surface of the nanoparticles react through different methods, for example, by self-assembly with products containing groups that when reacting may be more compatible with polymers and allow for better hydrophobic properties. In other words, by chemically modification functional groups are added to the nanoparticle surface to allow a better incorporation or compatibility with organic products such as polymers or other material matrix such as paper.
This type of nanoparticles is proposed in the Spanish Patent ES2354545 A1, which suggests the use of functionalized nanomaterials in the production of nanocomposites, to obtain different functional properties.
Below are abstracts and references of patents granted, patent applications and scientific publications considered in the analysis of the prior art associated with hydrophobic coatings for use on paper and board.
The U.S. Pat. No. 7,943,234 entitled “Nanotextured super or ultra hydrophobic coatings” describes a super-hydrophobic or ultra-hydrophobic coating composition that includes a polymer which may be a homopolymer or a copolymer of polyalkylene, polyacrylate, polymethyl acrylate, polyester, polyamide, polyurethane, polyvinlyl arilene, polyvinyl ester, copolymer of polyvinlyl arilene/alkylene, polyalkylene oxide or combinations thereof with particles having an average size of 1 nm to 25 microns, so that it favors a water contact angle of approximately 120° and 150 or more. In particular, the particle is silica which has been pretreated with a silane.
U.S. Pat. No. 7,927,458 entitled “Paper articles exhibiting water resistance and method for making the same” refers to a process for preparing a sticking paper and board that incorporates in its process a compound comprising one or more hydrophobic polymers, wherein the hydrophobic polymers, the amount of such polymers and the weight ratio of starch and such polymer in the compound may be selected so that the paper and board exhibit a Cobb value less than or equal to 25 g/m2 and a sticking paper or paperboard produced by the process.
U.S. Pat. No. 7,229,678 entitled “Barrier laminate structure for packaging beverages” describes a laminated packaging material which comprises from a first outer layer of a polymer of low density polyethylene, a board substrate, a first layer of inner laminated nylon lining with a resin bonding layer, an extrusion blown layer comprising a first layer of low density polyethylene polymer, a bonding layer, a first inner layer of EVOH, a second bonding layer, a second interior layer of EVOH, a third bonding layer, and a second inner layer of low density polyethylene polymer, and an innermost layer that is in contact with a product of low density polyethylene.
U.S. Pat. No. 6,949,167 entitled “Tissue products having uniformly deposited hydrophobic additives and controlled wettability” describe products containing a hydrophobic additive such as a polysiloxane. Additionally, paper products are further treated with a wetting agent.
U.S. Pat. No. 6,830,657 entitled “Hydrophobic cationic dispersions stabilized by low molecular weight maleimide copolymers, for paper sizing” refers to a method for preparing an aqueous dispersion of a hydrophobic polymer dispersed as particles with an average diameter smaller than 100 nm, stabilized only by a macromolecular surfactant based on an imide anhydride styrene/maleic copolymer of low molecular weight. It also refers to the use of said dispersion in the treatment of paper.
U.S. Pat. No. 6,187,143 entitled “Process for the manufacture of hydrophobic paper or hydrophobic board, and a sizing composition” refers to a process for the manufacture of hydrophobic paper or board by gluing colofine resin, a complex organic agent that is used together with the colofine resin. It also refers to a gluing composition. After the application of the hydrophobic additive on one or more surfaces of the base sheet, the wetting agent improves the wettability properties of the base sheet.
U.S. Pat. No. 5,624,471 entitled “Waterproof paper-backed coated abrasives” describes a waterproof paper coated abrasive made in a gluing machine comprising a binding agent curable by radiation which is hydrophobic when polymerized.
U.S. Pat. No. 4,268,069 entitled “Paper coated with a microcapsular coating composition containing a hydrophobic silica” describes a coating composition comprising oil containing microcapsules dispersed in a continuous aqueous phase, which also contains particles of finely divided silica phase and a binding agent for said microcapsules and said silica particles. The silica particles have been treated with an organic material such as an organic silicon compound to give the particles a hydrophobic surface. The coating composition is useful in the manufacture of paper coated with microcapsules. Such paper is characterized by a substantial reduction of the specking when used in photocopiers that use a pressure contact line to assist in transferring the powder image of a photoreceptor belt to the paper.
The patent application US20110008585 entitled “Water-resistant corrugated paperboard and method of preparing the same” describes a method for preparing waterproof corrugated board consisting of a corrugated medium treated with a hydrophobic agent on both sides and a lining treated with a hydrophobic agent on at least one surface side. The lining and corrugated medium are bonded by an adhesive prepared with a carrier of starch, raw starch, borax, a hydrophobic resin, an additive to improve penetration and water. The starch carrier is composed of cooked and raw starch. The lining and corrugated medium are treated with the hydrophobic agent before being glued. Hydrophobic resins include resorcinol formaldehyde and urea formaldehyde resins.
The patent application US20110081509A1 entitled “Degradable heat insulation container” describes a container including a container body made of paper, a waterproof layer and a layer of foam. The container body has an outer surface and an inner surface. The waterproofing layer is coated on the inner surface. The waterproofing layer is mainly composed of powdered talc, and calcium carbonate resin. The foam layer is disposed over at least a portion of the outer surface. The foam layer comprises reinforcements and a thermo-expandable powder. The binding agent is selected from a group consisting of polyvinyl acetate resin, ethylene resin, vinyl acetate resin, polyacrylic acid resin, and a mixture thereof. The thermo-expandable powder comprises a plurality of thermo-expandable microcapsules, each of which comprises a thermoplastic polymer shell and a solvent of low boiling point due to its thermoplastic polymer shell.
The patent application US20110033663 entitled “Superhydrophobic and superhydrophilic materials, surfaces and methods” describes a generally applicable method that requires no more than one step which facilitates the preparation of superhydrophobic or superhydrophilic surfaces of a large area on a variety of substrates such such as glass, metal, plastic, paper, wood, concrete, and masonry. The technique involves free radical polymerization of common acrylic or styrenic monomers in the presence of porogenic solvent in a mold or on a free surface.
The patent application US20100233468 entitled “Biodegradable nano-composition for application of protective coatings onto natural materials” refers to a method for producing a biodegradable composition containing cellulose nanoparticles to form a protective coating on natural materials. One of its objects is to provide a composition to form a protective coating layer on a natural biodegradable material which provides water resistance and grease resistance to the material. Another object is to provide a composition to form a protective layer to natural biodegradable materials based on the use of cellulose nanoparticles and protects these materials from swelling, deformations and mechanical damage during contact with water, other aqueous liquids, or fats.
The patent application US20100311889 entitled “Method for manufacturing a coating slip, using an acrylic thickener with a branched hydrophobic chain, and the slip Obtained” is a method for manufacturing a coated paper sheet containing a mineral material, using as an agent to thicken the sheet, a water-soluble polymer comprising at least one unsaturated ethylene anionic monomer and at least one unsaturated ethylene oxyalkyl monomer ending in a hydrophobic alkyl, alkaryl, arylalkyl chain, aryl, saturated or unsaturated, branched with 14 to 21 carbon atoms and two branches each, containing at least six carbon atoms. The polymer is added to the sheet either directly or in a previous stage when the mineral material is ground, dispersed or concentrated in water, which may or may not be followed by a drying step. Thus, the water retention of the barbotine is improved, contributing to improved printability of the coated paper sheet.
The patent application US20080188154 entitled “Film laminate” describes a laminate including at least one layer of environmentally degradable film, such as a polylactide (“PLA”) made from a readily available annually renewable polymer, from such resources as corn. A second layer may be a substrate made of, for example, paper, woven or non-woven fabric, or metal sheets. Environmentally degradable film and the substrate are adhered together by, for example, extruded polymers or adhesives such as water-based, hot melt, solvent or without solvent adhesives. The choice of the adhesive depends on the type of substrate to be laminated with environmentally degradable film and the desired properties of the resulting laminated composite structure (i.e., the “laminate”). The first layer is coated with a liquid polymer, a dispersion of nano-particles, a metal deposition or a silicone oxide deposition such that the gas permeability of the first layer is reduced. Said film laminates are used, for example, in packaging, envelopes, labels and forms printing, commercial publications, and in the digital printing industry.
The patent application US20080265222A1 entitled “Cellulose-Containing Filling Material for Paper, Tissue, or Board Products, Method for the Production Thereof, Paper, Tissue, or Cardboard Product Containing Such a Filling Material, or Dry Mixture Used Therefor” describes the surface modification of cellulose fibers with the application of nanoparticles to produce paper and packaging board. The advantage is in production and product recycling. Moreover, other different advantages are its acting as moisture repellent, adding whiteness and brightness to paper and board, biosida, antistatic and flame retardant. Nanodispersed cellulose and in combination with other components such as adhesives, polyvinyl sheets, flocculants, nanoparticle systems (not mentioned), polymers, anti-slip additives, an additive for fixation of the pigment, bleaches, defoamers, or preservatives.
The patent application US20080113188 entitled “Hydrophobic organic-inorganic hybrid silane coatings” describes a hydrophobic coating that may be formed from a solution that includes, for example, organically modified silicates mixed with coupling agents. Specifically, a sol-gel solution can be formed (i.e., at room temperature) which includes a plurality of alkoxysilane precursors containing at least one alkoxysilane glycidoxy precursor. The sol-gel solution may be a sol-gel mixed solution formed including by a first solution mixed with a second solution. The first solution may include one or more alkoxysilane glycidoxy precursors, and the second solution may include at least one alkoxysilane glycidoxy precursor. A coupling agent can be added and reacted with the sol-gel solution (mixed) forming the coating solution that can be applied to a substrate that needs to be protected against corrosion or chemical and/or biological agents.
In patent application US20080041542 entitled “Cellulose composites comprising hydrophobic particles and their use in paper products” composite polymeric films are proposed, prepared by solvent deposition of a suspension of quantum dots (QDs) in a solution of cellulose triacetate (CTA). The films were strong and had the correct optical properties of the quantum dots. The images obtained by Transmission Electron Microscopy (TEM) of the films revealed that the quantum dots are well dispersed within the matrix of the CTA film. Selective alkaline hydrolysis of QD/CTA films in NaOH 0.1 N for 24 hours resulted in the conversion of CTA surface to a regenerated cellulose. The optical properties of the films were tested both before and after the hydrolysis reaction using fluorescence spectroscopy, and found generally unchanged. Cellulose surfaces of the films allows superficial incorporation of alkaline treated films in the paper sheets.
The patent application US20030211050 entitled “Compositions comprising anionic functionalized polyorganosiloxanes for hydrophobically modifying surfaces and enhancing delivery of active agents to surfaces treated therewith” describes compositions and methods for treating and modifying surfaces and for enhancing delivery of active agents to surfaces treated therewith, wherein the compositions comprise siloxane polymers functionalized with outstanding fractions comprising two or more anionic groups, at least one anionic group which can be a carboxy group. When applied to a suitable surface, the present composition forms a layer of syloxane-anionic polymer substantially functionalized hydrophobic on the surface treated.
The patent application US20030012897 entitled “Liquid-resistant paperboard tube, and method and apparatus for making same” refers to a cardboard tube that becomes resistant to liquids by partial or complete coating of the tube with submicron-sized particles of inorganic materials treated to be hydrophobic and/or oleophobic. These particles can be applied directly to the board, settling in the surface pores such that the particles adhere to the board. Alternatively, a thin layer of a sticky binding agent or adhesive may be applied first to the board, and then the particles can be applied to adhere to the binding agent. Suitably, the particles have a large surface area per gram; in one embodiment, for example, the silica particles are employed having a surface area of about 90-130 m2/g. As a result, the particles create a surface on the board that is highly repellant to liquids.
The patent application US20030109617 entitled “Method for pretreatment of filler, modified filler with a hydrophobic polymer and use of the hydrophobic polymer” describes a modified filler used in the manufacture of paper or the like, the preparation of filler material and its use. The modified filler comprises a known filler such as calcium carbonate, kaolin, talc, titanium dioxide, sodium silicate and aluminum trihydrate or mixtures thereof, and a hydrophobic polymer made of polymerisable monomers, which is added to the filler as a polymer dispersion or a polymer solution.
The patent application US20020069989 entitled “Bonding of paper using latex-dispersions of copolymers made of hydrophobic monomers/polymers of styrene/maleic anhydride type of low molecular mass” describes latex dispersions used in formulations of a binder for paper which make it possible to obtain COBB acceptable values, even for printing and writing paper or wrapping paper made from recycling pulps or mechanically destined pulps.
The patent application US20020032254 entitled “Hydrophobic polymer dispersion and process for the preparation thereof” refers to a hydrophobic polymer dispersion and a solvent-free process for the preparation thereof. According to the invention, the dispersion contains starch ester, together with dispersion additives known as such. According to the process, the polymer is first mixed with a plasticizer to obtain a plasticized polymer blend. The plasticized polymer blend is then mixed with dispersion additives and water at an elevated temperature to form a dispersion. Plasticizing the polymer and the dispersion of the mixture in water can be performed in an extruder. The dispersion obtained is homogenized in order to improve its stability. The dispersion obtained by the invention can be used for coating paper or board, such as a base or a component of paint or adhesive labels, and is also suitable for the production of deposited films and as a binder in materials based on cellulose fibers, as well as for medicinal coating preparations.
The patent application WO2011059398A1 entitled “Strong nanopaper” refers to a nanopaper comprising clay and microfibrillated cellulose nanofibers in which the MFC nanofibers and the clay layers are substantially oriented parallel to the paper surface. The invention further refers to a method for manufacturing the nanopaper and its use.
The patent application WO2009091406A1 entitled “Coated paperboard with enhanced compressibility” refers to a coated paperboard with improved compressibility, which enables improved softness at a low surface pressure. The compressible coating is based on nanofibers having a diameter less than 1000 nm. One of the claims is that the rate of PakerPrint smootheness increases 1.2 units when the surface pressure increases 5 to 10 kgf/cm2. The procedure applies as described in TAPPI T555 om-99. The nanofibers can be: 1). Biopolymers: natural polymer, chitosan, a bicompatible polymer, polycaprolactone, polyethylene oxide, and combinations thereof. 2). Inorganic compounds: silica, aluminosilicates, TiO2, TiN, Nb2O5, Ta2O5, TiN oxide, among others. 3). Resins: such as polyester, cellulose ether and ester, polyacrylic resin, polysulphur, copolymers, etc. These nanofibers are in combination with a binder which may be a polymer selected from the group of polyvinyl alcohol, polyvinylpyrrolidone, and combinations thereof. The nanofibers can be improved by adding oleophobic and hydrophobic additives that can be compounded with fluorocarbon groups.
The patent application WO2008023170A1 entitled “Tailored control of surface properties by chemical modification” discloses a process for producing a polymer or an inorganic substrate which is capable of adhering more than one material by the functionalization of the surface linking to the substrate by a carbon precursor. Nanoparticles (fullerene C60 or nanotubes) present in an adhesive system comprising a polymer which can be selected from polyolefins, polyesters, epoxy resins, polyacrylates, polyacrylics, polyamides, polytetrafluoroethylene, polyglycosides, polypeptides, polycarbonates, polyethers, polyketones, rubbers, polyurethanes, polysulfones, polyvinyls, cellulose, and block copolymers.
The patent application WO2004035929A1 entitled “Method of producing a multilayer coated substrate having improved barrier properties” describes the production of a coated substrate that is forming a multilayer composite of free flow, with at least two layers with a different barrier function, and the contact mechanism of the compound to the substrate. The number of layers required will depend on the anti-barrier function. Laminar nanoparticles (not mentioned) which are immersed in a binding agent may be styrene-butadiene latex, acrylic styrene, acrylonitrile latex, maleic anhydride latex, polysaccharides, proteins, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, cellulose and its derivatives, among others. Claims for the coated substrate are: 1). Vapor transmission rate of less than 50 g/(m2/day). 2). Cobb value 10 minutes less than 20 g/m2. 3). Oxygen transmission value less than 200 cm3/(m2/d/bar) (1 atm, 23° C., 90% relative humidity).
The patent application WO2003078734A1 entitled “Composition for surface treatment of paper” describes a surface treatment of paper and cardboard with mixtures of inorganic nanoparticles and organic pigments in plate form, in an aqueous solution that act as hydrophobic agent, anti-foaming, whitening, improve paper print quality, and is also inexpensive. Silica nanoparticles and precipitated CaCO3, or mixtures of both. The nanoparticles are dispersed in latex (polymer) selected from the group: Butadiene-styrene, acrylate, styrene acrylate, polyvinyl acetate, and mixtures thereof.
The patent applications WO0076862A1 and ES2304963T3 entitled “Multilayer laminate structure of resin/paper, which contains at least one layer of polymer/nanoclay compound and packaging materials made thereof” describe a laminated structure for packaging and other applications than packaging, comprising: a paper substrate and at least one layer of polymer/nanoclay, comprising nanoclay particles with a thickness ranging from 0.7 to 9.0 nanometers applied to said paper substrate (4), wherein said layer of polymer/nanoclay compound consists of a mixture of a polymer resin with a barrier effect and a nanoclay, wherein said nanoclay is dispersed in the barrier polymer resin on a nanometer scale, and the amount of nanoclay in the composite layer represents from 0.5 to 7.0% in weight of the composite layer.
The patent CN1449913A entitled “Nano particle water-proof corrugated paper board” describes a corrugated waterproof paper. It consists of several layers of lined kraft cardboard and corrugated papers as raw materials that are placed between the Kraft liner sheets, respectively Said Kraft sheets and the raw materials are subjected to the process of oil immersion and to the treatment of moisture resistance, and subsequently protected by a microparticulate adhesive containing nano-calcium carbonate.
The patent application CN101623853A entitled “Full resin waterproof sand paper” describes a waterproof resin sandpaper, comprising six layers of an abrasive layer, an adhesive layer, a base layer for the adhesive, a surface layer of treated sandpaper, an original sandpaper layer, and a layer that is waterproof treated from top to bottom; wherein the adhesive layer is a mixture of urea formaldehyde resin, red iron and ammonium chloride, the base adhesive layer is a mixture of water-soluble acrylic resin, ammonium resin, fluoride and red iron; the treated surface layer of the sandpaper is a blend of latex rubber of nanometric styrene-butadiene, a solution of modified starch, water and penetrant JFS agent; the layer of waterproof treatment is a mixture of nanometric styrene-butadiene latex, a solution of modified starch, and a JFS penetrating agent.
The patent CN2871192Y entitled “The environmental protective decoration paper material”, describes a type of paper material for decoration and protection of the environment, which comprises corrugated cardboard on which a nano waterproof layer was set. The former corrugated cardboard is made of corrugated BE cardboard, and may have one or several BE cardboard sheets. The invention not only has the water- or flame-resistant functions, but also offers environmental protection and a low price.
The patent CN2557325Y entitled “Nano particle water-resistant corrugated board” describes a nano-particulate corrugated water-resistant cardboard by using the technology of nano-level calcium carbonate particles. The invention includes a plurality of layers of corrugated cardboard and leather, arranged between the leather layers. Leather layers and corrugated cardboard are joined by a link of calcium carbonate nanoparticles. The utility of the invention is directed to food packaging and transportation of large goods.
The patent application DE102004014483A1 entitled “Coating composition, useful for antimicrobially coating and providing antimicrobial properties to substrates (i.e., papers, textiles), comprises porous inorganic coating contained in a homogenous distribution and a cationic polysaccharide” describes an antimicrobial polymer coating whose matrix incorporates inorganic oxides improving the mechanical and antimicrobial properties. Said coating can be applied on substrates of paper or fabric and comprises an inorganic porous layer in a homogeneous distribution and a cationic polysaccharide. Nanosol SiO2, which is distributed evenly across a cationic polysaccharide.
The patent application JP2009173909A entitled “Process for production of cellulose nanofiber, and catalyst for oxidation of cellulose” mentions nanocellulose production from 4-hydroxy tempo derivatives which provide hydrophobicity.
The patent application JP2001163371A entitled “Packaging body having inorganic compound layer” refers to a method for improving the barrier properties to gases for a bottling body which consists in covering the bottling body with a sol-gel or a nanocomposite to create a film on the surface of the container which improves the gas impermeability properties.
The patent EP1925732A1 entitled “Packaging material with a barrier coating” describes a packing material for solid or liquid assets that contain paper, board, cardboard, cloth, wool, wood items, natural cellulose, plastic or compounds, which comprises a moisture resistant layer and active polymers with suspended microparticles and/or microclay. An independent claim is a method of manufacture (A) of a linear polymer coating, which occurs after the preparation of the base material, or in the separation process.
The patent EP1736504A1 entitled “Barrier materials and method of making the same” describes the barrier properties of an impervious material to water soluble gases is improved if the material is mixed with calcium carbonate nanoparticles which have a size of 10 to 250 nanometers. The barrier material is in a substrate to provide a substrate having properties of gas impermeability. A layer of heat sealable material can be applied to the exposed surface of the barrier material. It also discloses a method for manufacturing the coated substrate. The substrate can be paper, cardboard or paperboard.
In the article entitled “Development of superhydrophobic coating on paperboard surface using the Liquid Flame Spray”, Surface & Coatings Technology 205 (2010) 436-445, a method is described for generating nanoscale coatings in a continuous roll-to-roll process at atmospheric pressure. The nano-structured and transparent coating, based on titanium dioxide nanoparticles, was deposited successfully online under atmospheric conditions on pigment-coated cardboard using a thermal spray method called Liquid Flame Spray (LFS). The LFS coating process is described and the influences of process parameters on the quality of the coating are discussed. The nanocoating was investigated with a scanning electron microscopy of field emission scanning electrons (FEG-SEM), an atomic force microscope (AFM), a photoelectron spectroscope emitted by X-rays (XPS) and a measurement of water contact angle. The highest water contact angles on the surface of nano-coated cardboard were more than 160°. Falling water drops were able to bounce off the surface, which is illustrated with images of the high-speed video system. Despite the high hydrophobicity, the coating was of a sticky nature, creating high adhesion to the water drops as soon as the movement of the droplets was stopped. The nanocoating with complete coverage of the substrate occurred at line speeds up to 150 m/min. Therefore, the coating on the LFS shall expand the potential to an industrial level as an economical and efficient method for coating large volumes at high speed on line.
The article “Adjustable wettability of paperboard by liquid flame spray nanoparticle deposition”, Applied Surface Science 257 (2011) 1911-1917, describes the use of the process Liquid Flame Spray (LFS) for depositing nanoparticles TiOx and SiOx on cardboard to control the wetting properties of the surface. In the LFS process it is possible to create superhydrophobic or superhydrophilic surfaces. Changes in humidity are related to the structural properties of the surface, which were characterized by scanning electron microscopy (SEM) and an atomic force microscope (AFM). The surface properties can be assigned as a correlation between the properties of the cardboard moisture and surface texture created by the nanoparticles. The surfaces can be produced in line in a one-step process of roll-to-roll without further modifications. Moreover, the functional surfaces with adjustable hydrophilicity or hydrophobicity can be manufactured simply by choosing suitable precursor liquids.
The article “Modifications of paper and paperboard surfaces with a nanostructured polymer coating”, Progress in Organic Coatings 69 (2010) 442-454, describes organic synthesized nanoparticles by imidization of styrene/maleic anhydride copolymers, are deposited as the first layer on paper and cardboard substrates of a stable aqueous dispersion containing solids up to 35% by weight. The morphology, physicochemical characteristics and surface properties of the coatings are discussed in this document, using scanning electron microscopy, atomic force microscopy, measurements of water contact angle and Raman spectroscopy. Due to the high glass transition temperature of the polymeric nanoparticles, a single micro-structured coating on nanoscale forms to promote gloss improvement, printing properties (inkjet printing test and off-set printing test), surface hydrophobicity (with a maximum water contact angle of 140°) and water repellency (reduced Cobb values). The interaction of nanoparticles layers with the cellulose paper results in improved mechanic strength of the paper, and is attributed to hydrogen bonding between the nanoparticles and the cellulosic fibers.
As can be seen, the products that have been used, in general, are nanoparticles (dispersed in polymeric substrates) such as calcium carbonate, silicon oxide, titanium oxide, carbon nanotubes, fullerenes, among others.
Cellulose nanofibers derivatived from 4-hydroxy TEMPO, nanofibres of biopolymers, inorganic nanofibers or resins, are another type of nanomaterials used in the manufacture of paper and/or cardboard with hydrophobic properties. In some scientific articles the use of certain treatments was found such as the application of oxides of silicon or titanium through the process “Liquid Flame Spray”.
From the above and experimental evidence realized by the authors of the present invention, it is concluded that there are still opportunities for innovation and development of coatings based on nanoparticles enabling improved properties of paper and cardboard. For example, it is desirable that the coating after its application does not affect the printing of paper or cardboard, and it improves further the adhesion to the wings or bonding areas required by the cardboard boxes obtained. Moreover, it is desirable that the application of coatings on paper and cardboard do not prevent recycling of the corresponding packaging. From previous experiences with other products by the authors of the present patent application, it has also been found that the use of metal oxides such as silicon oxide, when not correctly functionalized require greater anchorage, and moreover, it is possible that they loosen with time causing the performance to be reduced during the handling of the packages.
To improve the performance of hydrophobic coatings on paper and cardboard, it is proposed in the present invention to use self-assembled silicon-oxide nanoparticles with silane based compounds and fluorocarbonated compounds, and alternatively the synergistic use of ultrasound to enhance the dispersibility of said silicon-oxide nanoparticles during their application on the fibers of at least one surface of the paper or cardboard.